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ACEEE Int. J. on Electrical and Power Engineering, Vol. 02, No. 01, Feb 2011 



A Novel Compensating Technique for Power Factor 
Improvement in Power Electronic Systems 



1 B . Jaganathan , 



C . Anuradha, 3R.Brindha, 4S . Vi jayalakshmi , 5 S . Pavithra 

1,2,3,4 ,5 EEE Department, SRM University, 

Kattankulathur, Kanchipuram(Dt),TamilNadu, INDIA. 

jagana78 @ gmail.com , 

anuradhac @ ktr. srmuni v. ac . in 

brindha aprl6@yahoo.co.in 

vijis india@ yahoo. coin 

pavithra. sreedharan @ gmail.com 



Abstract -Power electronics systems are non-linear systems, 
which consume more reactive power and also the loads they 
feed are mostly inductive loads which leads to a poor power 
factor. Various compensation techniques are available to bring 
the power factor nearer to unity. In this paper, a novel 
compensator is proposed, where in-phase and quadrature 
components of the supply current are vector-controlled. 
Implementation of this compensator in a power electronic 
system operating with a very poor power factor (and hence 
high THD), shows that the system then draws a leading 
current. A conventional power electronic system, A 
conventional power electronic system with one of the 
traditional static VAR compensators and the conventional 
power electronic system incorporated with the proposed 
compensator are simulated and the simulation results are 
obtained. It is shown that the proposed method offers only 
0.7% THD, which also implies that the power factor is 
improved. 

Keywords .-Total Harmonic Distortion, Vector Control, 
Compensator, Switching, Power Electronic Converters 

I.INTRODUCTION 

The Power Electronics converters have been 
increasingly employed in recent years owing to their 
advanced features including sinusoidal input current at unity 
power factor. Power electronic devices that have rapid and 
frequent load variations have become abundant today due 
to their many process control Supply side is developed. The 
in-phase component of the supply current I p is kept constant, 
whereas the quadrature component of the supply current I 
is controlled from the output of the speed loop. The vector 
control is formulated in d-q axis coordinated frame, the 
method requires on-line coordinate transformations that 
convert the line current in three related and energy saving 
benefits. These features are not necessarily achieved under 
the operating conditions of unbalanced input supply and 
input impedances. Such a generalized unbalanced operating 



condition is quite common in power systems, as the electrical 
energy is generated, transmitted in the form of alternating 
current. To meet this requirement, it is customary to add a 
power factor correction circuit. The low power factor is due 
to the power loads that are inductive which take lagging 
currents and hence lagging power factor [4] . To improve the 
power factor, device supplying reactive power are connected 
in parallel to the system at desired location. The capacitor 
draws a leading current and neutralizes the lagging reactive 
component of load current. This raises the power factor of 
the load. However they do not regulate the instantaneous 
power explicitly. So that it is not suitable for implementation. 
Various methods of VAR compensation are synchronous 
condensers, mechanically switched capacitors etc., [7,8] .With 
the advent of power electronic switches, TSC-Thyristor 
switched capacitor, has been used to absorb or inject reactive 
power[5,6]. 

This paper proposes a new control scheme in which 
a vector control method on the phase rotating frame to two 
phase synchronously rotating frame representation and vice 
versa [2], [3]. The d-q components of the input voltages 
and currents are employed to accurately describe the 
behavior of the converter. The proposed vector control 
scheme [1] allows the system to draw a leading current. 
Because the current is leading, THD is drastically reduced. 
Because of the growing concern about harmonic 
pollution there is a need to reduce the harmonic contents of 
the AC line current of power supplies. Harmonics may 
disrupt normal operation of devices. Therefore rapid reactive 
power changes demand timely reactive VAR compensation. 
Even with that, the THD is not up to the specified standards. 



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ACEEE Int. J. on Electrical and Power Engineering, Vol. 02, No. 01, Feb 2011 



II. CONVENTIONAL METHOD 

L 



Fi 


3f Rectifier 




Diveiler 




Inductive 
Load 


Yi 


II 








E 1 











Fig 1 A Power Electronics System with No 
Compensation Technique 

A power electronics system with no compensator 
is shown in fig 1 

The three phase supply is fed to the three phase rectifier 
which further, through a DC link feeds a three phase inverter. 
The load used is inductive or non-linear which will draw 
lagging current and hence poor power factor results. 




The phasor representation of this system is shown 
in fig 4. It can be noted that the power factor is improved 
than the conventional system. 

Since the power factor is improved the THD, i.e., 
the total harmonic distortion is reduced as these two have 
the inverse relationship. Also the drawback in this way of 
compensation is that the capacitance value can be changed 
in steps only. Though a dynamic Var compensator be used 
for PFC, it will have rotational losses, which will add up 
with the total losses 




costf) > cos 4>i 



Fig 2 Pliasor diagram of the System without 
C omp ensator 

The phasor representation of this system is shown in fig 2. It 
can be noted that the power factor is very poor. 



p* 








3it Rectifier 


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Inductive 

Load 


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B 1 


1 1 

1 1 


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1 










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: 













Fig 3 Power Electronics System with Static VAR 
Compensation 

A power electronics system with compensator at 
the supply side is shown in fig 3. The three phase supply is 
fed to the three phase rectifier which further, through a DC 
link feeds a three phase inverter. The load used is inductive 
or non-linear which will draw lagging current and hence 
poor power factor results. However because of the 
introduction of the compensator, the leading current drawn 
by the same also gets vectorially added with the load current 
and so the resultant current gets shifted towards the voltage 
phasor, i.e., the power factor is improved than the 
conventional system. 



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Fi£* 4 Phasor diagram of trie System wrtri 
Compensator 

III.THE PROPOSED METHOD 



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Fig 5 Power Electronics System with the proposed 
Compensator. 

The block diagram of a power electronics system is 
shown in the figure 5. As seen vector control is implemented 
on the supply side, i.e., the three phase currents are 
converted to two phase currents using Park's transformation 
and the control is implemented on to the rectifier control 
i.e., the switching of the rectifier. The rectifier then feeds 
the three phase inverter which further feeds the three phase 
inductive load. The phasor diagramsfor such a circuit are 
discussed in what follows. The current components I and 
I (I -the active component and I -the reactive component) 
are regulated by vector control. The orthogonal spatial 

orientation between I an I is achieved by unit vectors and 

p q J 



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ACEEE Int. J. on Electrical and Power Engineering, Vol. 02, No. 01, Feb 2011 



these unit vectors are generated from line voltage vector. 
Because VC is used, the appropriate 3phase-2phase and 
2phase-3phase transformation are done at appropriate 
places. The transformation equations from 3 phase 
synchronously rotating frame to 2 phase synchronously 
rotating frame and vice versa are given below. The 3phase 
voltages and 3 phase currents are sensed and individually 
(that is voltage and current) are transformed to 2 phase 
stationary frame voltages. This is obvious from the phasor 
diagram as shown in fig S6. 




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Fig 6 Plxa_sor diagram of tire proposed 
Sell erne during implementation 



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% 






(2/3) 



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cos(6-4i/3] sin (Mi/ 3] 0.707 



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w 



cose cos (8- 2i 1 3) cos(6-4t/3) 

sine sin(8-2i/3] Sill(9-4j/3) 

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cose cos [8- 2*/ 3) cos (6 - 4ic / 3) 

■sine -sin (6- 3k/ 3) -sin (9-4*/ 3) 
0.707 PJI 0.707 



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From this, 




V/=V CosG 

d s 


(i) 


V S =V sin 

q s 


(2) 


Cos9= V//V 

d s 


(3) 


sine =V S /V 

q s 


(4) 


in the 2 phase synchronously rotating frame 


i d =I P 


(5) 


K=\=° 


(6) 


L S =L cos6 

d P 


(7) 


i s = L sin9 

q p 


(8) 



Because of the particular switching, as apparent from the 
fig, the thyristors in the rectifier unit will conduct only for 
certain period at regular intervals. 

-> a! 




Fig 7 Resultant Phasor diagram of the 
Proposed scheme. 

This leads to reduced conduction losses and hence 
reduced heat losses. This adds to the improved efficiency of 
the system. The current component reactive power i.e. i * , 

where, . i * is the command value is set to zero and so, what- 

q 

ever be the reactive current component of the system (I ), 
the closed loop control will always try to make the total re- 
active current to be zero. Because an additional emf is also 
injected into the circuit and as a whole effect of vector con- 
trol and this emf, the power factor is improved much, i.e. it 
becomes a leading power factor or in other words, the cur- 
rent phasor leads the voltage phasor as shown in fig 7. 

IV. SIMULINK CIRCUITS 




Fig 8 Conventional system with no compensator 



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ACEEE Int. J. on Electrical and Power Engineering, Vol. 02, No. 01, Feb 2011 



A conventional power system is shown in fig. in 
which a three phase rectifier is fed by a three phase supply. 
Through a DC link the output of the rectifier is fed to a three 
phase inverter. A universal bridge is used in the inverter mode. 
A separate space vector generator circuit generates the space 
vector modulated signals which is fed as the input to the 
gates if the universal bridge. A highly inductive load is con- 
nected to the output of the inverter.For this typical system 
the input voltage and current waveforms are obtained and 
alsotheTHDis obtained which arediscussedinthelatersections. 




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ifif 




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Fig 9 Conventional system with static VAr 
Compensator 

A power system with a static VAr compensator at 
the supply side is shown in fig. in which a three phase 
rectifier is fed by a three phase supply. Through a DC link 
the output of the rectifier is fed to a three phase inverter. A 
universal bridge is used in the inverter mode. A separate 
space vector generator circuit generates the space vector 
modulated signals which is fed as the input to the gates if 
the universal bridge. A highly inductive load is connected 
to the output of the inverter. 

For this system the input voltage and 
current waveforms are obtained and also the THD is 
obtained which are discussed in the later sections. 




Fig 10 Conventional System with proposed 
Compensator 

The proposed novel compensator for a power 
system is shown in fig 10. The three phase supply is fed to 
a semi controlled converter and it is chosen because then 
the 

©2011 ACEEE 
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circuit will have an input current which is rich in harmonics, 
than when compared to a fully controlled rectifier. Through 
a DC link this semi converter feeds a three phase inverter 
(again an universal bridge is used). 

The input voltage and current in three phase 
synchronously rotating frame are then converted to voltage 
and current in two phase synchronously rotating frame. These 
voltages are then fed to a comparator where the other input 
to the comparator is the supply voltage itself. 

The error signal then decides the conduction of the 
switches in the semi converter. It is this feedback which 
decides the triggering of the appropriate switches. Of course 
the phase delay is the same as done in the traditional circuit. 

The inverter is given with SVM pulses for its gates. 
The load connected to the inverter is a highly inductive load 
which is one of the causes for poor power factor. 

IV TABULATION 



Ms 


Circuit 


%THD 
values 


i) 


Conventional system with no 
compensator 


95.85 


2) 


Conventional system with static 
VAR compensator 


93.60 


3) 


Conventional systemwiththe 
proposed novel compensator 


0,7 



Table 1 Percentage THD obtained with different 
Simulink circuits 

V WAVEFORMS AND OBSERVATIONS 

The waveforms of the above simulink circuits are 
shown in the following figures. The values of THD obtained 
with the above circuits are tabulated in table 1 . 

The input voltage and current waveforms of the 
conventional system is shown in fig 11 .It can be observed 
that the input current is non-sinusoidal and is rich in 
harmonics whose THD value is 95. 85%. Also the THD 
obtained with this system is shown in fig 12. 

The input voltage and current waveforms of the 
conventional system with static Var compensator is shown 
in fig 13. Even here the input current is non-sinusoidal and 
is rich in harmonics and its THD value is 93.60%, shown 
in fig 14. 

In the figure 15, is shown the input voltage and 
input current waveforms of the conventional system 
incorporated with the proposed compensator. The THD is 
also shown in fig. 16 where the THD value is only 0.7% 
and this is because the input current is leading with respect 
to the input voltage. 



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ACEEE Int. J. on Electrical and Power Engineering, Vol. 02, No. 01, Feb 2011 




80 
70 

I 50 

a 

m 

E 20 

10 




Fig 1 1 Input Voltage and Current waveforms of the 
conventional system with no compensator 

Fundamental (5GHz) = 1 .383S-KBE , THD= 95.85% 



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1000 



2000 3000 J0O0 

Fnquency (Hz) 



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SODO 6000 7000 



Fig 12 THD of the system without 
Compensator 




Fig 13 Input Voltage and Current waveforms of the 

Conventional system with static VAr 

Compensator 



30 








Fundamental (50Hz) = 1 339ei005 , THD= 93.60% 






70 






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100 200 300 400 500 ODD 700 
Frequency (Hz) 



Fig 14 THD of the conventional system with 
Static VAr Compensator 



900 1000 




Fig 15 Input Voltage and Input Current waveforms 
of the system with proposed compensator 





Fundamental pjHz) = 0.04672 , THD= 0.70% 




02 

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o 01 

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0.05 





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in 


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100 200 300 400 900 600 7D0 HE 900 10 

Frequency (Hi) 


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Fig 16 THD of the proposed system with novel 
compensator. 



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ACEEE Int. J. on Electrical and Power Engineering, Vol. 02, No. 01, Feb 2011 



VI. CONCLUSIONS 

A novel compensating technique for the 
improvement of power factor in non-linear electrical 
systems such as power electronic systems is presented in 
this paper. Vector control is implemented at the supply side 
of the system. .The reactive component of the supply current 
is set to zero which is then compared with the actual reactive 
component of current that is drawn by the system. With the 
closed loop control the system starts drawing a leading 
current which implies that the power factor is improved 
and so the Total Harmonic Distortion is reduced. A 
conventional system, a conventional power system with 
static Var Compensator, and a typical power system with 
the proposed technique are simulated using MATLAB/ 
SIMULINK and the waveforms of input voltage and input 
current and the THD for each of them are obtained and 
compared. It is observed that with the proposed method, 
the entire system starts drawing a leading current inspite 
of the non-linear loads connected to the system(the system 
itself is a non-linear one). The THD value is also found to 
be reduced to a great extent. 



VII. REFERENCES 

[1] Bimal K.Bose," Modern Power Electronics and AC drives" 
PHI publications 2005 

[2] Yongsug Suh, Valentin Tijeras, and Thomos A.Li "A Control 
method in dq Synchronous Frame for PWM Boost Rectifier 
under Generalized Unbalanced Operating onditions", IEEE 
PESC Conference,Queensland, Australia, June 23-27, 2002 

[3]Enjeti, PN.Zioga. P D.Lindsay. J. F. Rashid, M.H Anew PWM 
speed control system for high Performance AC motor drive 
"IEEE Transactions on Industrial electronics, 1997. 

[4]Holtz J; Springob L, "Reduced harmonics PWM controlled line- 
side converts for electric drives",IEEE transactions on Industry 
applications. Volume 29, No.4, July 1993. PP 814-819. 

[5]Akagi,.H. — Kanazawa,Y. — Nabae, "Instantaneous Reactive 
Power Compensators Comprising Switching Devices without 
Energy Storage Components", IEEE Trans on Ind. Appl. IA-20 
No. 3 (May/June 1984). 

[6]Akagi,H. — Kanazawa,Y. — abae, A., "Generalized Theory of the 
Instantaneous Reactive Power in Three-Phase Circuits", IPEC, 
Tokyo'83,pp. 1375-1386. 

[7]Bowes, S. R. — Clements, R. R., "Computer Aided Design of 
PWM Inverter Systems", IEE. Proc.129, Pt. B Nol (Janl982). 

[8] Patel, H. S. — Hoft, R. G "Generalized Technique of Harmonic 
Elimination and Voltage Control in Thyristor Inverters Part I- 
Harmonic Elimination", IEEE Trans. On Ind. Appl. IA-9(May/ 
June 1973), 310-317. 



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